Nearly all electronic and optical devices require patterning. Patterned metals are used in forming a variety of such devices. For example, patterned metals may be used in forming transistors, as electrodes in various devices, and as shadow masks in the patterning of various materials. One possible use for patterned metals is as electrodes in organic light emitting devices (OLEDs), which make use of thin films that emit light when excited by electric current. Popular OLED configurations include double heterostructure, single heterostructure, and single layer, and may be stacked, as described in U.S. Pat. No. 5,707,745, which is incorporated herein by reference in its entirety.
Patterning of sub-micrometer structures is preferable for the realization of new and improved types of devices such as flat panel displays.
For OLEDs from which the light emission is only out of the bottom of the device, that is, only through the substrate side of the device, a transparent anode material such as indium tin oxide (ITO) may be used as the bottom electrode. Since the top electrode of such a device does not need to be transparent, such a top electrode, which is typically a cathode, may be comprised of a thick and reflective metal layer having a high electrical conductivity. In contrast, for transparent or top-emitting OLEDs, a transparent cathode such as disclosed in U.S. Pat. Nos. 5,703,436 and 5,707,745 may be used. As distinct from a transparent or bottom-emitting OLED, a top-emitting OLED is one which may have an opaque and/or reflective substrate, such that light is produced only out of the top of the device and not through the substrate, or can be a fully transparent OLED that may emit from both the top and the bottom.
As used herein, the term “organic material” includes polymers as well as small molecule materials that may be used to fabricate OLEDs. The organic materials of an OLED are very sensitive, and may be damaged by conventional semiconductor processing. For example, any exposure to high temperature or chemical processing may damage the organic layers and adversely affect device reliability.
Electronics based on organic semiconductors can be realized on a wide range of substrates, including light-weight flexible plastics and metal foils. Owing to this property, there is intense interest in the realization of low-cost, large-area electronics using organic materials. However, the weak van der Waals intermolecular bonding in the organic layers makes them too fragile to withstand conventional photolithographic processes which can involve exposure to solvents and high energy plasmas. Furthermore, to fully utilize the advantageous features of these materials, alternative low-cost patterning techniques need to be developed. It has been demonstrated that metal electrodes for organic electronics could be patterned by locally transferring a metal film either from a substrate to a ‘stamp’, (C. Kim, P. E. Burrows, and S. R. Forrest, Science 288, 831 (2000)) or vice versa (C. Kim, M. Shtein, and S. R. Forrest, Appl. Phys. Lett. 80 (21), 4051 (2002)) using cold-welding between the metal films predeposited onto both contacting surfaces. Among these techniques, an additive method using elastomeric stamp (C. Kim and S. R. Forrest, Adv. Mater. 15 (6), 541 (2003)) is most attractive due to its low pressure patterning capability. However, the integration of various devices on the same substrate requires direct patterning of active organic materials, as well as electrodes. For example, the fabrication of full color displays usually requires separate depositions through a shadow mask for each emitting material, and the use of a pre-patterned integrated shadow mask for cathode isolation.